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Modern machinery manufacturing technology is developing towards high efficiency, high quality, high precision, high integration and high intelligence. Precision and ultra-precision processing technology has become an important part and development direction of modern machinery manufacturing, and has become a key technology to improve international competitiveness.
1. Clamping of turning tool
1) The extension of tool holder should not be too long, the general length should not exceed 1.5 times of the height of the tool holder (except for holes and grooves)
2) The center line of turning tool bar should be perpendicular or parallel to the cutting direction.
3) Adjustment of tool tip height:
A, the end face, taper surface, thread, forming surface and cutting solid workpiece, the tip of the tool should generally be equal to the axis of the workpiece.
B, rough car outer circle, fine car hole, tip should be slightly higher than the axis of the workpiece.
C. When the slender shaft, thick hole and hollow workpiece are cut, the tip of the tool should be slightly lower than the axis of the workpiece.
4) Bisector of thread turning tool tip Angle should be perpendicular to the axis of the workpiece.
5) When clamping the tool, the gasket under the tool rod should be less and flat, and the screw of the pressing tool should be tightened.
2. Workpiece clamping
1) with three jaw self-centering chuck clamping workpiece for rough or fine car, if the diameter of the workpiece is less than 30㎜, the suspension length should not be greater than 5 times the diameter, if the diameter of the workpiece is greater than 30㎜, the suspension length should not be greater than 3 times the diameter.
2) with four jaw single action chuck, flower plate, Angle iron (bent plate) and other clamping irregular weight workpiece, must add counterweight.
3) When processing shaft workpiece between apex tips, the apex apex axis of tailstock should be adjusted to coincide with the spindle axis of the lathe before turning.
4) When processing slender shaft between two tips, follow tool rest or center rest should be used. Pay attention to adjust the top in the process of processing
Tip tension, dead tip and center frame should be lubricated.
5) When using the tailstock, the sleeve should be extended as short as possible to reduce vibration.
6) when clamping the workpiece with small supporting surface and high height on the vertical car, the high clamping claw should be used, and the workpiece should be pressed by the rod or plate at the appropriate part.
7) When turning the casting and forging parts of wheel and sleeve, it shall be adjusted according to the unprocessed surface to ensure the uniform wall thickness of the workpiece after processing.
3. Turning processing
1) When turning step shaft, in order to ensure the rigidity of turning, the part with larger diameter should be turned first and the part with smaller diameter should be turned after.
2) When cutting slots on the shaft workpiece, it should be carried out before finishing to prevent deformation of the workpiece.
3) fine car with thread shaft, generally should be in the thread processing and then fine car without thread part.
4) Before drilling, the end face of the workpiece should be leveled. If necessary, hit the center hole first.
5) When drilling deep holes, the guide holes are usually drilled first.
6) turning (φ 10 - φ 20) hole, the diameter of the knife rod should be processed aperture 0.6-0.7 times; Processing diameter is greater than 20 mm hole, generally should be used to clamp the knife head.
7) When turning multi-thread or multi-worm, trial cutting should be carried out after adjusting the exchange gear.
8) when using automatic lathes, the relative position of the tool and the workpiece should be adjusted according to the machine tool adjustment card, and the trial turning should be carried out after the adjustment, and the first qualified piece can be processed; Pay attention to tool wear and workpiece size and surface roughness during machining.
9) When turning on a vertical lathe, when the tool rest is adjusted, the beam shall not be moved at will.
10) When the workpiece surface position tolerance requirements, try to complete the turning in a clamping.
11) When turning the cylindrical gear blank, the hole and the reference end face shall be processed in a clamping process. If necessary, a marking line should be drawn near the gear indexing circle of the end face.
4. Error compensation
Modern machinery manufacturing technology is developing towards high efficiency, high quality, high precision, high integration and high intelligence. Precision and ultra-precision processing technology has become an important part and development direction of modern machinery manufacturing, and has become a key technology to improve international competitiveness.
With the wide application of precision machining, turning machining error has become a hot research topic. As thermal error and geometric error occupy the vast majority of errors in machine tools, so to reduce these two errors especially the thermal error has become the main goal. Error compensation technology appears and develops with the development of science and technology. The losses caused by thermal deformation of machine tools are considerable.
It is necessary to develop a high precision and low cost thermal error compensation system to correct the thermal error between the spindle (or workpiece) and the cutting tool, so as to improve the machining accuracy of machine tools, reduce waste products, increase production efficiency and economic benefits.
(1) Basic definition
Error compensation is the basic definition of artificially created a new error to offset or current become less problem of original error, through the analysis, statistics, induction and grasp the characteristics and regularity of the original error, error of mathematical model is set up, make man-made error and the original error of both equal and opposite, thus reducing the machining error, improve dimensional precision parts.
Earlier error compensation was achieved by hardware. Hardware compensation belongs to mechanical fixed compensation. When the error of machine tool changes, parts, ruler or compensation mechanism must be re-made to change the compensation amount. Hardware compensation can not solve the randomness error, lack of flexibility. Recently developed software compensation is characterized by using modern advanced technology and computer control technology to improve the machining accuracy of machine tools without any change in the machine tool itself. Software compensation overcomes many difficulties and shortcomings of hardware compensation and pushes the compensation technology to a new stage.
(2) Characteristics
Error compensation (technology) has two main characteristics: scientific and engineering.
The rapid development of scientific error compensation technology has enriched the theory of precision machinery design, precision measurement and the whole precision
Secret engineering has become an important branch of this discipline. The related technology of error compensation includes detection technology, sensing technology, signal processing technology, photoelectric technology, material technology, computer technology and control technology. As a branch of new technology, error compensation technology has its own independent content and characteristics. It is of great scientific significance to further study the error compensation technology to theorize and systematize it.
The engineering significance of engineering error compensation technology is very significant, which contains three meanings: first, error compensation technology can easily achieve the precision level that "hard technology" can cost a lot to achieve; Second, error compensation technology can solve the accuracy level that "hard technology" usually cannot reach; Third, if the error compensation technology is used to meet certain accuracy requirements, the cost of instrument and equipment manufacturing can be greatly reduced, with very significant economic benefits.
5. Generation and classification of thermal errors in turning processing
With the further improvement of machine tool accuracy, the proportion of thermal error in the total error will continue to increase, and the thermal deformation of machine tool has become the main obstacle to improve machining accuracy. Machine tool thermal error is mainly caused by thermal deformation of machine tool components caused by internal and external heat sources such as motor, bearing, transmission parts, hydraulic system, ambient temperature, coolant and so on. The geometric error of machine tool comes from the manufacturing defect of machine tool, the matching error between machine tool components, the dynamic and static displacement of machine tool components and so on.
Basic error compensation methods:
To sum up, the turning error is generally caused by the following factors: thermal deformation error of machine tools; Geometric errors of machine tool parts and structures; Error caused by cutting force; Tool wear error; Other error sources, such as machine tool shafting servo error, nc interpolation algorithm error and so on. There are two basic methods to improve the accuracy of machine tools: error prevention and error compensation.
Error prevention is an attempt to eliminate or reduce possible error sources by means of design and manufacturing. Error prevention method is effective in reducing temperature rise of heat source, equalizing temperature field and reducing thermal deformation of machine tool to a certain extent. However, it is impossible to eliminate thermal deformation completely and the cost is very high. The application of thermal error compensation method opens up an effective and economical way to improve the accuracy of machine tools.
The research of turning processing error is an important part and development direction of modern machinery manufacturing, and has become the key technology to improve the international competitiveness. The generation of error is in many aspects, and the analysis and research of thermal error is conducive to improve the turning accuracy and technical requirements.
The thermal error compensation technology can correct the thermal drift error between the spindle (or workpiece) and the cutting tool, improve the machining accuracy of machine tools, reduce waste products, increase production efficiency and economic benefits.
6. Frequently Asked Questions
Common lathe in the strong turning of large pitch thread, sometimes there will be bed saddle vibration, light to make the surface of the processing ripple, heavy knife break. When cutting off, there is often a knife or broken knife phenomenon. There are many reasons for the above problems. This paper mainly discusses this phenomenon and its solution through analyzing the force of the cutting tool.
Causes and causes of the problem:
When turning the thread pitch is small, the direct cutting method is generally used (in the direction perpendicular to the axis of the workpiece to do the straight cutting); When turning the thread with larger pitch, in order to reduce the cutting force, the left and right tool cutting method is often adopted (by moving the small slide plate so that the thread turning tool is respectively cut with the left and right cutting edges).
When turning the thread, the bed saddle is moved by the rotation of the lead screw to drive the movement of the opening nut to achieve. The bearing of the lead screw has an axial clearance, and there is also an axial clearance between the lead screw and the opening and closing nut. When using left and right tool cutting method strong
When cutting dextral worm with the right main blade, the tool is subjected to the force P from the workpiece (the friction between chip and front cutter is ignored, as shown in Figure 1), and the force P is decomposed into axial component Px and radial component Px. The axial component Px is the same as the feed direction of the tool, and the tool sends the axial component Px to the bed saddle. Thus promote the bed saddle to have a gap to do fast and violent back and forth movement, the result is to make the tool back and forth movement, and make the processing surface ripple, and even broken knife. However, when cutting with the left main blade, there is no such phenomenon. When cutting with the left main blade, the axial component Px of the tool is opposite to the feed direction and moves in the direction of eliminating the gap, and the bed saddle moves at a uniform speed.
When cutting off, the movement of the slide plate is realized by rotating the screw of the slide plate to drive the movement of the nut. There is an axial clearance at the bearing of the lead screw, and there is an axial clearance between the lead screw and the nut. On the lathe cutting, tool rake face () with anterior horn of the workpiece under P to its force, (ignore the chip and the rake face friction, as shown in figure 2), the force P Pz into force and radial force, the radial component force and the cutting tool of feed in the same direction, pointing to the workpiece, push the tool towards the workpiece, which would pull the slide to a gap in direction of motion, Make the cutting knife suddenly tie artificial parts, causing tie (break) knife or workpiece bending.
Solutions:
When turning pitch larger about borrow knife cutting method of screw thread, in addition to adjust the lathe related parameters, should also adjust the fit clearance between the saddle with bedway, make it a little tight, in order to increase big move when the friction force, reduced the likelihood of bed saddle up to move, but can't adjust the gap is too tight, with shaking bed saddle smooth advisable.
Adjust the clearance of the skateboard, so that the clearance is small as far as possible; Adjust the tightness of the small skateboard to make it slightly tighter to prevent the turning tool from shifting when turning. Should shorten the workpiece and the length of the tool bar, as far as possible to use the left main blade cutting; When cutting with the right main blade, the back draught should be reduced; Increase the front corner of the right main blade. The edge of the blade should be straight and sharp to reduce the axial component Px of the tool. Theoretically, the larger the front Angle of the right main blade, the better.
